from collections import Counter

c = Counter()
with open('/usr/share/doc/gdb-7.6.1/COPYING.LIB', 'rt') as f:
    for line in f:
        c.update(line.rstrip().lower())

print('Most common:')
for letter, count in c.most_common(4):
    print('{}: {:>7}'.format(letter, count))
